The present invention generally relates to a storage apparatus and its control method, and, for instance, can be suitably applied to a storage apparatus that drives one or more hard disk drives for storing data.
In recent years, demands from job sites of information business such as data centers for storing data reliably and on a long-term basis are increasing. For example, the law prohibits the deletion of document data of financial institutions and medical institutions, and such data must be accumulated.
Under these circumstances, a highly reliable large-capacity storage system is required. With a large-scale storage system using hard disk drives, generally speaking, power consumption will increase in proportion to the storage capacity. In other words, to own a large-capacity storage system means increase in the power consumption.
Nevertheless, storage systems are constantly demanded of reliable and long-term storage of data as well as further reduction of power consumption. In light of these circumstances, when it is necessary to accumulate large volumes of data and in certain cases to store such data for a long period of time, storage of data in an appropriate storage position in response to various demands sought in the stored data is effective in reducing the power consumption of the overall storage system.
Incidentally, as conventional art in this kind of technical field, for instance, Non-Patent Document 1 (“Power-efficient Server-class Performance from Arrays of Laptop Disks”, Athanasios E. Papathanasiou and Michael L. Scott, The University of Rochester, Computer Science Department, Rochester, N.Y. 14627, Technical Report 837, May 2004 [URL searched on Sep. 25, 2006] http://www.cs.rochester.edu/u/papathan/papers/2004-usenix04/usenix04-wip/papath an-usenix04-wip-summary.pdf) proposes technology of shutting off the hard disk drive during normal times, and operating the hard disk drive corresponding to a data storage extent upon receiving an I/O request from a host system.
In addition, Patent Document 1 (Specification of U.S. Patent Application No. 2004/0054939) and Non-Patent Document 2 (“The Case for Massive Arrays of Idle Disks (MAID)”, Dennis Colarelli, Dirk Grunwald and Michael Neufeld, University of Colorado, Boulder, FAST'02, USENIX [URL searched on Sep. 25, 2006] http://www.usenix.org/publications/library/proceedings/fast02/wips/colarelli.pdf) propose a storage system applying MAID (Massive Arrays of Idle Disks) technology for realizing a storage system of low power consumption.
Moreover, in recent years, a flash memory is attracting attention as a nonvolatile memory. A flash memory is generally of a power consumption that is several ten times lower in comparison to a hard disk drive, and enables high-speed reading. Further, a flash memory can be configured in a compact size since it does not require a mechanical drive unit as in a hard disk drive, and the tolerance against malfunctions is generally high.
Nevertheless, a flash memory has a limited write cycle due to physical reasons of the cells retaining the information. To overcome this kind of limitation, technology referred to as wear-leveling adjustment for retaining the correspondence of the address and cell position to be indicated to the host system and equalizing the number of writings into the respective cells is used to seek improvement in the write cycle of the flash memory. Incidentally, the elemental device for retaining information is hereinafter simply referred to as a “flash memory”, and the elemental device including a mechanism for performing the foregoing wear-leveling adjustment and protocol processing to the host system is hereinafter referred to as a “flash memory device”.
With a flash memory device, although efforts are being made to seek the efficiency in the write cycle restrictions with the foregoing technology, this does not mean that the restrictions on the write cycle will be completely eliminated. In addition, when an operation referred to as deletion is required during the writing [of data] into the flash memory, this process is performed at roughly the same speed as a hard disk drive.
Incidentally, as conventional art in this kind of technical field, for instance, Patent Document 2 (Japanese Patent Laid-Open Publication No. 2004-164193) proposes a storage system of switching the flash memory and the hard disk drive during a failure in a hybrid hard disk drive.
Nevertheless, with the storage system of Non-Patent Document 1, since the hard disk drive is operated after receiving the I/O request, there is a problem in that a delay in the response time will arise until the storage system replies to the host system, whereby the access performance will deteriorate.
Further, Patent Document 1 and Non-Patent Document 2 are limiting their application to storage systems that will not encounter any problems even when the access performance deteriorates, and do not give any consideration to a technological solution for the deterioration in the access performance. Thus, they do not realize the simultaneous pursuit of low power consumption and maintenance of high access performance.
In addition, although Patent Document 2 proposes the switching of the flash memory and the hard disk drive when a failure occurs in the hybrid hard disk drive, it does not realize the simultaneous pursuit of low power consumption and maintenance of high access performance.
Accordingly, it is necessary to realize a storage system capable of reducing power consumption while maintaining high access performance which could not be achieved with the conventional technology described above. In particular, although data centers and the like are increasingly demanding lower power consumption, it would be meaningless to lower the power consumption with a method that would deteriorate the access performance that is originally required.
Thus, the task would be to provide a storage system that applies a flash memory to realize the simultaneous pursuit of low power consumption and maintenance of high access performance that could not be achieved by conventional technology.